400 DISEASES OF THE SKIN. 



The male acari and the young parasites generally inhabit cavi- 

 ties in the skin which they have made for themselves. These 

 cavities are connected externally by short ducts, the entrances 

 of which may be marked by small vesicles or pustules, while the 

 females may move to different parts of the body when sexually 

 ripe, burrowing ducts through the upper layers of the epidermis 

 down as far as the membrana Malpighii, which contains a great 

 deal of fluid. At the end of the duct — that is, the place of entrance 

 of the acari — we see the development of a small, somewhat moist 

 nodule — or a vesicle, which dries up ultimately, leaving a scar. 

 This digging of the parasite may produce more or less detachment 

 of the epidermis. We generally find that the parasite has a prefer- 

 ence for certain parts of the body, such as the head, neck, abdomen, 

 and chest, at the root of the tail, and the paws. It is very hard to 

 detect it with the microscope. The best way is to remove some of 

 the membrane with the scissors or scrape the upper portion of the 

 skin to the corium. If parasites have been present for some time 

 a secondary eczema is soon developed, which is produced by 

 scratching and rubbing, also by itching of the scabs and scales. 

 This " mange eczema" appears in various forms, according to the 

 sensitiveness of the skin, and is either papular, vesicular, or pus- 

 tular, and sooner or later produces decided thickness of the skin 

 and leads to the formation of a number of folds, wrinkles, and 

 ulcerated points between the clefts of the wrinkles. There is 

 always a certain characteristic appearance about these affected 

 localities which makes it easy to distinguish between the para- 

 sitic and simple eczema. The surfaces finally become confluent, 

 forming large eczematous areas. It is very improbable that a 

 mistake will be made in diagnosis, except in the early stages, 

 when there is only a very small spot affected, because the para- 

 sitic eczema produces rapid characteristic changes, accompanied 

 by scratching, twitching, rubbing, and licking, which are very 

 much aggravated as soon as the animal is placed near any warm 

 object — for instance, in the neighborhood of a stove or if covered 

 up with a blanket, and also the evident pleasure which the 

 animal gets if the affected part is rubbed or scratched; and 

 finally, if the animal is kept with other dogs, the disease is carried 

 to them and developed very quickly. The disease can also be 

 produced in man by taking a mangy scab and applying it to the 



